The present invention relates to detergent compositions which contain selected anionic surface-active agents together with polyester soil-release copolymer, and which contain, at most, only limited amounts of specific types of incompatible anionic surface-active agents. These compositions clean soiled fabrics, and provide a soil-release benefit for both greasy/oily and body soils (such as facial, collar and cuff soils) on synthetic fabrics, particularly polyesters, when used in an aqueous laundering system. The detergent compositions herein permit the use of the disclosed soil-release polymers together with surfactant systems containing a broad range of surface-active agents. In addition, the compositions herein tend to inhibit the redeposition of soils onto fabrics during the laundering operation, and also improve the water absorption characteristics of polyester garments, thereby affording the wearer greater comfort.
Much effort has been expended in designing compositions which are capable of conferring soil-release properties to fabrics woven from polyester fibers. These fibers are mostly copolymers of ethylene glycol and terephthalic acid, and are sold under a number of trade names, for example, Dacron, Fortrel, Kodel, and Blue-C Polyester. The hydrophobic character of polyester fabrics makes their laundering, particularly as regards oily soils and stains, difficult, principally due to the inherently low wettability of the polyester fibers. Since the character of the fiber itself is hydrophobic (or oleophilic), once an oily soil is deposited on the fabric, it becomes bound to its surface. As a result, the oily soil or stain is difficult to remove in a conventional aqueous laundering operation.
It is well-recognized that an oily soil is much more easily removed from a hydrophilic fabric, such as cotton, than it is from a hydrophobic polyester fabric. This difference in oil removal characteristics is apparently caused by the greater affinity of cotton fabrics for water and surfactant.
The differing hydrophilic/hydrophobic characteristics of cotton and polyester are due in part to the basic building blocks of the fibers themselves. Since polyester fibers are copolymers of terephthalic acid and ethylene glycol, they have less affinity for water because they possess fewer free hydrophilic groups, i.e., hydroxyl or carboxyl groups, where hydrogen bonding can occur. With cotton, which is a cellulose material, the large number of hydrophilic groups provides compatibility with, and affinity for, water.
In terms of detergency, the most important difference between hydrophobic and hydrophilic fabrics is the tendency for oily soils to form easily removable droplets when present on a hydrophilic fabric in contact with water and surfactant. The mechanical action of washing and the action of synthetic detergents and builders, normally used in the washing step of the laundering process, removes such oily droplets from the fabric. This droplet formation is in contrast to the situation which exists with a polyester hydrophobic fiber. Since water does not wick well through hydrophobic fabrics, the oily soil tends to be retained throughout the fabric, both because of the inherent hydrophobic character of the fabric and the lack of affinity of oily soils for water.
Since polyester and polyester blend fabrics, such as polyester/cotton blends, are popular and are susceptible to oily staining, manufacturers of polyester fibers and fabrics have sought to increase the hydrophilic character of the polyester, in order to provide ease of laundering for the consumer.
A variety of approaches to the problem of increasing the hydrophilic character of polyester fabrics and fabric blends has been taken. Many of these approaches involve a treating process employed by the fiber or textile manufacturer. For example, U.S. Pat. No. 3,712,873, Zenk, issued Jan. 23, 1973, discloses the use of polyester polymers, in combination with quaternary ammonium salts, as fabric-treating compositions. Terpolymers having a molecular weight in the range of from 1,000 to 100,000 and a terephthalic acid:polyglycol:glycol molar ratio of about 4.5:3.5:1 are disclosed. These compositions are applied by spraying or padding them onto textiles containing polyester or polyamide synthetic materials, for the purpose of improving the soil-release characteristics of these materials. U.S. Pat. No. 3,959,230, Hays, issued May 25, 1976; U.S. Pat. No. 3,479,212, Robertson et al, issued Nov. 18, 1969; and U.S. Pat. No. 3,416,952, McIntyre et al, issued Dec. 17, 1968, also disclose the use of ethylene terephthalate/polyethylene oxide terephthalate copolymers in the manufacture or treatment of polyester articles, for the purpose of providing them with enhanced hydrophilic character, and hence improved removal of oily soils.
It has been suggested that soil-release polymers may be incorporated into detergent compositions, so that when polyester-containing fabrics are washed in aqueous solutions of these compositions, the fabrics will be modified in order to improve the removal, upon subsequent washing, of oil-containing stains. Even if the fabrics are treated by the manufacturer, the treatment benefit is diminished as the fabrics age, mainly due to removal of the soil-release polymer through washing in ordinary detergent products. Thus, the use of detergent compositions containing soil-release polymers provide laundered fabrics with an ongoing soil-release benefit. U.S. Pat. No. 3,962,152, Nicol et al, issued June 8, 1976, discloses the use of specific low ratio ethylene terephthalate/polyethylene oxide terephthalate copolymers in solid detergent compositions.
The use of relatively high ratio ethylene terephthalate/polyethylene oxide terephthalate soil-release polymers together with nonionic surfactants, in detergent compositions, is known in the art. British Patent Specification No. 1,377,092, Bevan et al, published Dec. 11, 1974, teaches the use of such copolymers in detergent compositions containing nonionic surfactants. It is indicated that the presence of anionic surfactants in those detergent compositions should be avoided, since such surfactants decrease the soil-release properties of the compositions. Further, U.S. Pat. No. 4,020,015, Bevan, issued Apr. 26, 1977, discloses a process by which terephthalate copolymers or cellulose ether soil-release agents are dispersed in a water-soluble, detergent-compatible carrier, for use in a granular laundry detergent composition. Once again, it is taught that the presence of anionic surfactants in such compositions decreases soil-release performance.
The use of nonionic surface-active agents in solid-form detergent compositions, particularly spray-dried detergent compositions, presents various processing and packaging problems. Nonionic surfactants tend to be oily and, thus, exist as a separate phase when placed in a crutcher mix, prior to spray-drying. Such nonhomogeneity in the crutcher mix is intolerable when preparing a homogeneous spray-dried detergent granule. Further, in terms of packaging, the presence of large amounts of nonionic surfactant in a detergent composition may cause the surfactant component to wick through the package or container holding the composition. Thus, there are clear advantages in the use of anionic, instead of nonionic, surfactants in such laundry detergent compositions. Copending U.S. Patent application Ser. No. 699,412, Nicol, filed June 24, 1976, discloses detergent compositions, containing ethylene terephthalate/polyethylene oxide terephthalate soil-release copolymers, which may also contain anionic surfactants. However, these compositions require the presence of free hardness or other cations in the laundry solution in order to yield adequate soil-release performance. It has now been found that by using particularly selected anionic surfactants together with the soil-release copolymers, built anionic laundry detergent compositions, which are particularly effective in producing a soil release effect for oily soils on hydrophobic fabrics, may be formulated.
It is a primary object of this invention to provide detergent compositions which exhibit excellent cleaning performance while concurrently imparting soil-release properties to hydrophobic fabrics laundered therewith, and which do not require the presence of free hardness or other cations in the laundry solution to achieve this result.
It is another object of this invention to provide detergent compositions which inhibit the redeposition of soils onto fabrics during the laundering operation, and which additionally enhance the water absorption capacity of polyester garments.
It is yet another object of this invention to provide anionic surfactant-containing detergent compositions which may be fully built, and which contain specifically defined ethylene terephthalate/polyethylene oxide terephthalate soil-release ingredients.
It is a further object of this invention to provide detergent compositions comprising soil-release polymers having specific molar ratios of ethylene terephthalate and polyethylene oxide terephthalate.
It is a further object of this invention to provide a laundering method for the improved removal of oily soils from hydrophobic fibers.